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R. G. ZIMBELMAN and L. W. SMITH

Summary.

The effects of oral melengestrol acetate (mga) on ovarian activity have been studied in 264 dairy and beef heifers. A total of ninety-eight heifers received 0·4 mg of mga daily for short periods of time (18 to 32 days) and ovarian activity was determined by rectal palpation. As the incidence of a detectable corpus luteum decreased from 76 % to 10 %, the incidence of a detectable follicle increased from 56 % to 91 %. Follicular size also increased with time. Samples of cervical mucus were rated according to fern pattern, which was interpreted as due to an oestrogenic influence, and which occurred upon regression of the corpus luteum even though oestrus and ovulation were inhibited by mga treatment.

A total of 166 beef heifers was used in long-term studies (105 to 116 days) of mga treatment. Significant (P<0·05) increases were found in the weight of follicular fluid, primarily of the largest follicle from the pair of ovaries. Also indicative of increased oestrogenicity was an increased adrenal weight in puberal, intact mga-treated heifers. The adrenal weights of spayed heifers tended to decrease with mga treatment. The optimal dose for increased follicular activity appears to be near 0·4 mg mga daily/heifer.

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L. W. SMITH and R. G. ZIMBELMAN

Summary.

Sixty-four normally cycling Holstein heifers were randomly assigned into four equal groups (three treatment and one control). Each of the three treatment groups received 0·5 mg of melengestrol acetate (MGA®) daily and a single injection of either oestradiol cypionate (ECP®), human chorionic gonadotrophin (hcg) or pituitary luteinizing hormone (plh) between Days 22 and 26 following oestrus or Days 8 to 12 of MGA feeding. The control animals received neither MGA nor an injection. Heifers from each treatment group were spayed (overiectomized) on Days 2, 5, 8 and 11 from the injection and control heifers were spayed on Days 1, 4, 7 and 10 from oestrus. The corpora lutea (cl) and the largest follicles on the ovaries of each heifer were observed for size and colour.

Oestrus was observed in only the ECP-treated group within 24 hr following the injections (nine of sixteen animals). Ovulation occurred following the injection in all of the sixteen animals in the hcg group and in fifteen of the sixteen animals in each of the ECP and plh groups. All the control heifers ovulated following oestrus.

Normal cl were present in all the treated heifers spayed by Day 5. On subsequent days, increasing numbers of heifers had cl which were regressing.

The percentages of heifers spayed on Day 8 and Day 11 after injection with regressing cl were: 0% and 50% for the ECP group; 25% and 100% for the hcg group; and 75% and 50% for the plh group. All the heifers in the control group had normally developing cl regardless of the day of spaying.

The follicles from those animals which had regressing cl were generally larger than those from control heifers.

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R. G. ZIMBELMAN and L. W. SMITH

Summary.

Dairy heifers with normal oestrous cycles were treated with progestagen for 15 to 18 days beginning at the 15th day of the cycle. Daily oral doses of 0·25 to 8 mg of melengestrol acetate (6α-methyl-6-dehydro-16-methylene-17-acetoxyprogesterone: mga) inhibited oestrus and ovulation in all heifers except one receiving 0·5 mg. Daily intravenous injections of 0·4 mg inhibited ovulation in eight out of eight heifers. Lower doses by either route suppressed oestrus but did not uniformly inhibit ovulation. Orally, mga was about 300 to 900 times as potent as map (medroxyprogesterone acetate; Provera*) but only about ten to fifteen times as potent when both were compared by intravenous injection.

Groups of eight to ten heifers were fed doses of 0·2 to 2·0 mg daily beginning without regard to the stage of the oestrous cycle. Of seventy-two heifers, sixty-nine did not ovulate during treatment. The average interval from last feeding to oestrus or ovulation ranged from 2·7 days at 0·2 mg to 6·3 days at 2·0 mg. The conception rates for various groups varied from 25 to 88 % at first service. Of the total, 42 % conceived with one service and 82 % with two services.

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L. W. SMITH and R. G. ZIMBELMAN

Summary.

Sixty-three dairy and beef heifers were given single intravenous (i.v.) injections of 2, 5 or 10 mg of oestradiol cypionate (ECP®) during, on the last day, or on Day 1 or Day 2 after last feeding of melengestrol acetate (MGA®). Thirty-five heifers, which were used as controls, were fed MGA for intervals corresponding to those given ECP. The dairy heifers were checked for pregnancy by rectal palpation 35 to 45 days after service, but the beef heifers were slaughtered following breeding. Reproductive tracts were grossly examined for abnormalities and the oviducts were flushed for ova. Data were collected from both groups on the occurrence of oestrus, ovulation and on conception rate.

ECP increased the overall incidence of oestrus. Ovulation, however, did not appear to be greatly affected by ECP, although there was a slight tendency for ovulation to occur sooner after oestrus in the heifers given ECP. ECP appeared to have a detrimental effect on the conception rate at the first controlled breeding, but the conception rate at subsequent breedings appeared normal. The reduced conception rate at first service following MGA plus ECP treatment appeared to be due to multiple causes: ovulation failure, ovum loss, fertilization failure and embryonic death. ECP would appear to have a favourable effect only when oestrus and/or ovulation failure was the primary cause of reduced conception rate.

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L. W. SMITH and R. G. ZIMBELMAN

Summary.

The following compounds were used in an effort to induce oestrus and ovulation in Holstein dairy heifers during melengestrol acetate (MGA®) treatment: oestradiol cypionate (ECP®), oestradiol-17β, Carbestrol®, human chorionic gonadotrophin (hcg), pituitary luteinizing hormone (plh), pregnant mare serum gonadotrophin (pmsg), oxytocin, neostigmine, amphetamine, nafoxidine hydrochloride and clomiphene citrate. MGA feeding began on Day 15 of the oestrous cycle and continued for 15 to 20 days. All the above compounds were administered between Day 8 and Day 13 of MGA feeding. The compounds were given by various routes of administration. Only the oestrogens (ECP, oestradiol-17β and Carbestrol) effectively induced oestrus and ovulation, their effectiveness seeming to depend on the method of administration and the type of vehicle in which they were administered. ECP was effective at 5, 10 and 20 mg when injected intravenously (i.v.) in an oil vehicle. Oestradiol-17β was effective at 10 mg when injected intramuscularly (i.m.) in an oil vehicle. Both were less effective when the vehicle was propylene glycol. Carbestrol was effective only when given orally at 40 mg and 60 mg levels.

The gonadotrophins (hcg, plh and pmsg) did not produce consistent results. When the follicles disappeared, a subsequent corpus luteum did not always appear to develop.

The other compounds tested had no observable effect on oestrus or ovulation.

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J. L. Juengel, G. W. Smith, M. F. Smith, R. S. Youngquist and H. A. Garverick

Although the decrease of progesterone in serum and in luteal tissue during luteal regression is well characterized, relatively little is known about changes in proteins produced by the corpus luteum during this time. The first objective was to examine changes in patterns of protein secretion that might be associated with functional and structural luteal regression. The second objective was to characterize the expression of two major secretory products of regressing corpora lutea. Thirty normally cyclic heifers were randomly assigned at day 15–16 of the oestrous cycle (oestrus = day 0) to be ovariectomized at 0 h (no PGF; n = 5) or at 4, 8, 12, 24 or 48 h after PGF-induced luteal regression (n = 5 per time point). Total cellular RNA was isolated from tissue frozen at the time of ovariectomy. Thin slices (< 1 mm) of tissue were placed in methionine-deficient minimum essential media with [35S]methionine and placed in a humidified CO2 incubator at 38°C. Media and tissues were collected 6 h later. Changes in profiles of secreted proteins were analysed by one-dimensional SDS-PAGE. A number of proteins (relative molecular mass ranging from 14 300 to 200 000) were produced by luteal tissue at each time point (0–48 h). The major secretory proteins had relative molecular masses of approximately 21 500, 28 200, 43 700 and 46 000. Secretion of the relative molecular mass 46 000 protein(s) increased (P < 0.05) between 4 and 24 h after PGF injection compared with the 0 h group. Western blot analyses with either tissue inhibitor of metalloproteinase-1 or tissue inhibitor of metalloproteinase-2 antisera detected immunoreactive proteins of relative molecular mass 28 200 and 21 500, respectively. Concentrations of mRNA encoding tissue inhibitor of metalloproteinases-1 increased (P < 0.01) by 8 h after PGF injection, remained stable (P > 0.20) through 24 h and decreased (P < 0.05) by 48 h after PGF. Concentrations of tissue inhibitor of metalloproteinases-2 mRNA were highest (P < 0.05) at 8 h after PGF injection and lowest (P < 0.05) 48 h following induction of luteolysis. In summary, the profile of luteal protein production changed during luteolysis and two secretory products (tissue inhibitor of metalloproteinases-1 and -2) were identified. Metalloproteinase inhibitors may have an important role in tissue remodelling during structural luteolysis.

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K. M. Smith, P. C. W. Lai, H. A. Robertson, R. B. Church and F. L. Lorscheider

Summary. Maximal concentrations of AFP, measured by RIA, were obtained in fetal plasma and amniotic and allantoic fluid between the 3rd and 4th month of gestation, with levels declining thereafter until term. AFP values in maternal plasma were unchanged. Throughout gestation, AFP values were higher in allantoic than in amniotic fluid and the ratio of allantoic fluid/amniotic fluid AFP was significantly correlated with gestational age.

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R. N. Kirkwood, K. R. Lapwood, W. C. Smith and I. L. Anderson

Summary. Piglets were weaned from multiparous sows at 10 days (Group E; N = 7) or 35 days (Group C; N = 8) of lactation. Blood samples were collected at 8 h intervals from the day before weaning (Day – 1) until and including the day of first mating, then once daily until 10 days post coitum. Additionally, 5 sows in each group were sampled at 30 min intervals for 12 h on Days – 1, 0 and 1, then at 30 min intervals for 6 h daily until mating, finally at 30 min intervals for 2 h daily until 5 days post coitum. Group E sows had relatively longer weaning to remating intervals (8·3 ± 0·8 compared with 5·0 ± 0·7 days; P < 0·01) and tended, but not significantly, to produce smaller subsequent litters (10·2 ± 1·9 compared with 12·0 ± 0·6). Sows in group E had lower lactational and post-weaning plasma LH levels (P < 0·001). They also had greatly attenuated preovulatory LH rises and the area under the peak was reduced (P < 0·01 and P < 0·001, respectively). Preweaning plasma prolactin levels were higher at 9 days of lactation than at 34 days and levels in both groups dropped precipitously subsequent to piglet removal. Although peak levels of prolactin at oestrus did not differ between treatments, they tended to occur before the LH peak in sows of Group C and after the LH peak in Group E. No treatment differences were detected in plasma levels of oestradiol-17β or progesterone. These results suggest that the poorer reproductive performance of sows after a very short lactation is due, at least in part, to a reduced release of LH at the first post-weaning oestrus.

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P. Smith, W-S. O, N. L. Hudson, L. Shaw, D. A. Heath, L. Condell, D. J. Phillips and K. P. McNatty

The aim of this study was to determine whether the FecB gene influenced some aspects of fetal development in sheep. Carrier (BB/B+) and non-carrier (++) female fetuses were recovered at specific times of gestation, namely, days 40, 55, 75, 90, 95 and 135. The results showed that the FecB gene influenced litter size, body weight and ovarian development during fetal life. The mean litter sizes were larger (P < 0.05) and body weights were lighter (P < 0.05) at most gestational ages in BB/B+ than in ++ fetuses. Morphometric studies of the ovary showed that the development of the BB/B+ ovaries was retarded: the ++ genotype had more oogonia at day 40 (P < 0.01), more germ cells entering meiosis at day 55, more primordial follicles developing at days 75, 90 and 95 (P < 0.05), a greater loss of germ cells by atresia at day 90 (P < 0.01) and more growing follicles (P < 0.01) and more antral follicles (P < 0.05) at day 135. Differences between the BB/B+ and ++ genotypes in the plasma concentrations of immunoreactive (i) inhibin, i-FSH, bioactive (b)-FSH or (i)-LH were not apparent at any age except for i-LH at day 75 (BB/B+ > ++; P < 0.05). Likewise no differences were noted in the contents of ovarian or adrenal oestradiol or i-inhibin except for i-inhibin in the adrenal at day 75 (++ > BB/B+, P < 0.01). No differences between the genotypes were noted in the i-inhibin contents of the mesonephros at day 40. In mid- to late but not early gestation (i.e. days 40 and 55) significant correlations (i.e. P < 0.05) were noted between litter size and body weight at days 75, 90 and 135, and between litter size and ovary weight, ovary volume, adrenal weight and pituitary weight at day 135. To eliminate the effect of litter size, equal numbers of BB/B+ and ++ embryos were transferred to respective recipient ewes, and fetuses were recovered at the equivalent of days 40 and 90 of gestation. The results showed that the genotypic difference in fetal body weight at day 40 (++ > BB, P < 0.001) and in number of oogonia at day 90 (++ > BB/B+, P < 0.05) were independent of litter size. We hypothesize that many of the differences between the Booroola genotypes in ovarian follicular development and pituitary function in neonatal and adult life may be a consequence of differences in the timing or rate of body weight or organ development in fetal life.

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L. S. Leshin, S. M. P. Raj, C. K. Smith, S. C. M. Kwok, R. R. Kraeling and W. I. Li

Pig seminal proteins PSP-I and PSP-II are major protein components of boars' ejaculate and are present as heterodimers (PSP-dimer) in seminal plasma. These proteins were examined for their ability to modulate pig lymphocyte activity in vitro in mitogen-induced lymphocyte proliferation assays and in one-way mixed lymphocyte reactions. Pig lymphocytes were cultured with phytohaemagglutinin, concanavalin A, or pokeweed mitogen (PWM) in the presence or absence of pig seminal proteins and the amount of cellular [3H]thymidine was used as an indication of proliferation. In the absence of mitogens, none of the three pig seminal proteins affected lymphocyte proliferation suggesting that these proteins are not antigenic or mitogenic. PSP-dimer enhanced lymphocyte proliferation induced by PWM (156–227%, P < 0.05) in a concentration-dependent manner, but had no effect on phytohaemagglutinin- or concanavalin A-induced proliferation. PSP-I enhanced (127–185%, P < 0.05) phytohaemagglutinin-induced proliferation. PSP-II augmented (130–240%, P < 0.05) lymphocyte proliferation induced by concanavalin A and PWM. Lymphocytes from gilts were significantly more responsive to concanavalin A- and PWM-induced lymphocyte proliferation in the presence of PSP-I compared with boars (concanavalin A: gilts 131%, boars 91%; PWM: gilts 188%, boars 134%; P < 0.05). In the mixed lymphocyte reaction, pretreating stimulating cells with increasing concentrations of PSP-I or PSP-II elicited a 400% concentration-dependent increase (P <0.01) in lymphocyte proliferation. The abundance of pig seminal proteins in boar seminal plasma, their ability to enhance lymphocyte proliferation, and their previously reported ability to bind to lymphocytes suggest that these proteins are immunostimulatory and supports the hypothesis that they modulate uterine immune activity to ensure reproductive success.